ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 30

• Manufacturer Part Number: ADT7473
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7473
Disabling Fan Startup Timeout
Although fan start-up makes fan spin-ups much quieter than
fixed-time spin-ups, the option exists to use fixed spin-up
times. Setting Bit 5 (FSPDIS) to 1 in Configuration Register
(0x40) disables the spin-up for two TACH pulses. Instea
fan spins up for the fixed time a
Register 0x5E.
PWM Logic State
The PWM outputs can be programmed high for a 100% duty
cycle (noninverted) or low for a 100% duty cycle (inverted).
PWM1 Configuration Register (0x5C)
Bit 4 INV.
0 = ogic high for a 100% PWM duty cycle
1 = ogic low for a 100% P
PWM2 Configuration Register (0x5D)
Bit 4 INV.
0 = L
1 = L
PWM3 Configuration Register (0x5E)
Bit 4 INV.
0 = Logic high for a 100% PWM duty cycle
1 = Logic low for a 100% PWM duty cycle
Low Frequency Mode PWM Drive Frequency
The PWM drive frequency can be adjusted for the application.
Register 0x5F to Register 0x61 configure the PWM frequency
for PWM1 to PWM3, respectively. In high frequency mode, th
PWM drive frequency is always 22.5 kHz.
High Frequency Mode
Setting Bit 3 of Register 0x5F enables high frequency mode
all fans.
PWM Frequency Registers (Register 0x5F to Register
0x61)
Bits [2:0] FREQ
L
L
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz
100 = 35.3 Hz (default)
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
ogic high for a 100% PWM duty cycle
ogic low for a 100% PWM duty cycle
PWM Drive
WM duty cycle
s selected in Register 0x5C to
d, the
for
1
Rev. A | Page 30 of 76
e
Fan Speed Control
The ADT7473 contro
modes.
In automatic fan speed control mode, fan speed is automatically
var d with temperature and without CPU interven
ini l parameters are set up. The advantag
sys m hangs, the user is guaranteed the sy
fro overheating. The automatic fan speed control incorp
a f ture called dynamic T
the d
con rol loop. For more information and procedures on how to
prog
T
Co trol Loop section.
In manual fan speed control mode, the ADT7473 allows the
duty cycle of any PWM output to be manually adjusted. Thi
can be useful if the user wants to change fan speed in softwa
or adjust th
[7:5] of Register 0x5C to Register 0x5E (PWM co
registers) control the behavior
PWM Configuration Registers (Register 0x5C to
Register 0x5E)
Bits [7:5] BHVR
Once under manual control, each PWM output can be ma
ally updated by writing to Register 0x30 to Register 0x
current duty cycle registers).
Programming the PWM Current Duty Cycle Registers
The PWM current duty cycle registers are 8-bit registers that
allow the PWM duty cycle for each output to be set anywhere
from 0% to 100% in steps of 0.39%.
The value to be programmed into the PWM
Example 1: For a PWM duty cycle of 50%
Example 2: For a PWM duty cycle of 33%
PWM Current Duty
Register 0x30, PWM1 Duty Cycle = 0x00 (0% default)
Register 0x31, PWM2 Duty Cycle = 0x00 (0% default)
Register 0x32, PWM3 Duty Cycle = 0x00 (0% default)
MIN
ea
tia
te
m
n
ie
t
ram the automatic fan speed control loo
111 = manual mode
Value (decimal) = PWM
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) o
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 0x54 (hex)
esign effort required to program the automatic f
calibration, see the Programming the Automatic Fan Speed
e PWM duty cycle output for test purposes. Bits
ls fan speed using automatic and manual
Cycle Registers
MIN
r 0x80 (hex)
MIN
calibration. This feature red
of each PWM output.
/0.39
e of this is that, if the
MIN
stem is protected
p and dynamic
register is given by
nfiguration
tion, once
an speed
32 (PWM
uces
orates
nu-
s
re